Properties of supersonic cold gas jets for space probe moving

The properties of a supersonic free jet are analyzed experimentally and theoretically. A number of very different generating conditions are presented; for each case, the propellant characteristics are compared as well as the corresponding translational parameters. The translational relaxation processes occurring in the free jet expansion are described by solving a set of equations derived from die first four moments of the Boltzmann equation. The usual approximation of a spherical expansion is amended by including a pseudo-isentropic description of the shape of the flow tubes, in order to obtain an effective cooling of the longitudinal translational temperature, as obtained experimentally. This method is applied to the expansion of pure gas or binary gas mixtures (purely monatomic or including H-2 molecules), generated from room temperature, oven temperature, or plasma stagnation conditions. In any case, the agreement with the measured terminal velocity and longitudinal temperature is lather good, and the energy balance is satisfied within a few percent.